Trachoma is a chronic ocular disease caused by Chlamydia trachomatis. it is the second leading cause of blindness worldwide. To date no vaccine has been proven to be efficacious in a clinical setting. While topical antibiotic preparations are effective against the chlamydia organism, previous large-scale treatment efforts have been disappointing. The objective of this proposal is to develop a systematic treatment program to prevent blindness from trachoma based on a detailed understanding of the dynamics of the transmission of chlamydia. This understanding will be achieved by using the approaches of molecular epidemiology and epidemiological modeling. The following specific questions will be answered: l) Does previous infection with chlamydia offer any protection against subsequent reinfection? 2) Is the apparently inevitable recurrence of chlamydial infection after initially effective treatment, secondary to reinfection or to within-host persistence of the original organism? 3) How effective would a vaccine have to be to eliminate trachoma in endemic areas? 4) What is the most effective use of antibiotic treatment in decreasing the incidence of trachoma? As a Mentored Clinical Scientist Training program, this proposal also aims to develop the research abilities of the PI, and enable him to be a productive independent researcher.